Physical vapor deposition (PVD) or sputter deposition is a frequently used processing technique in the manufacturing of semiconductor devices that involves the deposition of a metallic layer on the surface of a semiconductor device. The physical vapor deposition technique is more frequently known as a sputtering technique. In more recently developed semiconductor fabrication processes, the sputtering technique is used to deposit metallic layers of tungsten or titanium tungsten as contact layers.
In a sputtering process, inert gas particles such as those of argon or nitrogen, are first ionized in an electric field to produce a gas plasma and then attracted toward a source or a target where the energy of the gas particles physically dislodges, i.e., sputters off, atoms of the metallic or other source material. The sputtering technique is very versatile in that various materials can be deposited utilizing not only RF but also DC power sources.
In a typical sputter chamber, the major components utilized include a stainless steel chamber that is vacuum-tight and is equipped with a helium leak detector, a pump that has the capacity to reduce the chamber pressure to at least 10.sup.-6 torr or below, various pressure gauges, a sputter source or target, a RF or DC power supply, a wafer holder, a chamber shield and a clamp ring. The sputter source is normally mounted on the roof of the chamber such that it faces a wafer holder positioned in the center of the chamber facing each other. The sputter source utilized can be a W or TiW disc for a process in which W or TiW is sputtered. A typical sputter chamber is that supplied by the Applied Materials, Inc. of Santa Clara, Calif. under the trade name of Endura.RTM. 5500. In some of the sputter chambers, the wafer holder is structured as a pedestal which includes an internal resistive heater.
One of the more important component in the sputter chamber is the clamp ring which serves two purposes during a sputter process. The first purpose is to clamp the wafer to the pedestal heater. The clamp ring holds the wafer in place on the pedestal when a positive gas pressure is applied between the heater and the pedestal such that heat can be efficiently conducted from the heater to the wafer. The second purpose served by the clamp ring is to allow a predetermined flow of argon to leak from under the wafer into the sputter chamber. The clamp ring is generally constructed in a circular shape with an oriented cut-out to match a wafer's flat contour. A hood is built into the clamp ring and is used for shadowing purpose to protect the lip of the clamp ring from being coated by the sputtered metal particles. The lip portion also allows the force of the clamp ring to be evenly distributed around the wafer.
A cross-sectional view of a typical sputter chamber 10 is shown in FIG. 1. Sputter chamber 10 is constructed by a stainless steel chamber body 12 that is vacuum-tight, a sputter target 16 of W, TiW or Sn, a wafer holder 20 equipped with a heater 22, a wafer lift mechanism 24, a wafer port 28, a pumping port 32, a clamp ring 30 and a chamber shield 34. A DC power supply 25 is connected to a target 21 and a conductive part of the chamber, such as the chamber wall 18 or chamber shield 34, thereby establishing a voltage potential between the grounded chamber wall 18 and the target 21. A DC bias circuit 23 is connected to the clamping ring and thus applies a DC bias to the wafer (not shown). A perspective view of the clamp ring 30 and the chamber shield 34 is shown in FIG. 1A. An enlarged, partial cross-sectional view of the clamp ring 30 and the chamber shield 34 is shown in FIG. 1B. The hood 36 of the clamp ring 30 protects the tip 38 from being coated by the sputtered particles.
As shown in FIG. 1, the chamber shield 34 is another important component in the sputter chamber 10. It forms a seal between the clamp ring 30 and the chamber body 12 such that sputtered particles from the sputter target 16 do not contaminate the chamber wall 18 during a sputtering process. It should be noted that, during the sputtering process, the wafer pedestal 20 is in a raised position with the tip portion 38 of the clamp ring 30 touching the heater 22 on the pedestal 20. In order to achieve a tight seal from the chamber wall 18, a small gap 40 is normally maintained between the clamp ring 30 and the chamber shield 34.
In a typical metal sputtering process where a W, TiW, Sn or other metal target is used in the sputter chamber, the emission of sputtered particles of the metals is shaped with a forward cosine distribution such that a more desirable deposition process in which metal particles are deposited uniformly at the center and the edge of the wafer can be achieved. However, due to the small gap 40 maintained between the clamp ring 30 and the chamber shield 34, and after successive deposition processes have been conducted in the chamber, a distortion in the chamber shield 34 may lead to arcing problems occurring in the chamber. The arcing problem may occur in one of two situations. First, after the reactant gas such as Ar or N.sub.2 is flown into the chamber, thermal expansion between already distorted parts further reduces the gap between the clamp ring and the chamber shield such that arcing occurs. The second situation occurs after plasma is turned on to ignite a plasma cloud of the metal particles. Since plasma generates a large amount of heat, a distorted chamber shield may further expand to reduce its distance from the clamp ring and thus cause arcing. When arcing occurs under either circumstances, severe damage in the form of particle contamination can occur on the wafer positioned on the pedestal which can cause a significant part of the wafer or even the entire wafer to be scrapped.
Sputter chamber designers have attempted to prevent arcing problem in a sputtering process by making modifications to the chamber component. However, none of these modifications have proven to be effective in reducing distortions in the components after successive usage of the chamber and thus the arcing problem can not be effectively controlled.
It is therefore an object of the present invention to provide a novel method and apparatus for preventing arcing in sputter chambers that do not have the drawbacks and shortcomings of the conventional method and apparatus.
It is another object of the present invention to provide an apparatus for preventing arcing in a sputter chamber by providing a ground detection circuit to the chamber hardware such that a grounding condition of the wafer pedestal can be effectively detected prior to the occurrence of arcing.
It is a further object of the present invention to provide an apparatus for preventing arcing in a sputter chamber equipped with ground detection circuits for detecting the existence of a grounding condition between a clamp ring and a chamber shield.
It is another further object of the present invention to provide an apparatus for preventing arcing in a sputter chamber by providing separate ground detection circuits for detecting the existence of a grounding condition during a reactant gas flow process and during a plasma deposition process.
It is still another object of the present invention to provide an apparatus for preventing arcing in a sputter chamber by utilizing a ground detection circuit for detecting the occurrence of a grounding condition such that a power supply to the sputter chamber can be interrupted prior to the occurrence of arcing.
It is yet another object of the present invention to provide an apparatus for preventing arcing in a sputter chamber by utilizing a first ground detection circuit for detecting a grounding condition during a reactant gas flow process, a second ground detection circuit during a plasma ignition process, and an interlock circuit for receiving signals from either one of the ground detection circuits such that a power supply to the sputter chamber can be interrupted prior to the occurrence of arcing.
It is still another further object of the present invention to provide a method for preventing arcing in a sputter chamber by providing a first ground detection circuit, a second ground protection circuit and an interlock circuit such that a power supply to the sputter chamber can be interrupted when a grounding condition is detected by the detection circuits.
It is yet another further object of the present invention to provide a method for preventing arcing in a sputter chamber by monitoring the magnitude of a DC bias voltage on a wafer pedestal during a reactant gas flow process and during a plasma ignition process.